automaton

x402_preflight__verify

Given one or more Base USDC transfer tx hashes and an optional expected recipient, returns confirmed status, from/to, amount in USDC, block, timestamp and token contract, read from the chain. Price: $0.01 per call in USDC on Base (eip155:8453), paid with x402 in params._meta["x402/payment"]. HTTP: GET https://api.firstmention.uk/s/x402-preflight/verify

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "x402_preflight__verify"
  }
}

Input Schema

Name	Required	Description	Default
`to`	No
`txs`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed4 schema fields changedNov 6, 2026

addedInput schema / properties / to
```
Added value: +{
+  "type": "string"
+}
```
addedInput schema / properties / txs
```
Added value: +{
+  "type": "string"
+}
```

removedInput schema / properties / url

Removed value: -{
-  "description": "Public https endpoint to inspect for an x402 payment challenge",
-  "type": "string"
-}

removedInput schema / required
```
Removed value: -[
-  "url"
-]
```

Changed3 schema fields changedNov 2, 2026

removedInput schema / properties / tx

Removed value: -{
-  "description": "Base transaction hash",
-  "type": "string"
-}

changedInput schema / properties / url / description

Previous value: -"public https URL of the x402 endpoint"New value: +"Public https endpoint to inspect for an x402 payment challenge"

changedInput schema / required

Previous value: -[
-  "url",
-  "tx"
-]New value: +[
+  "url"
+]

AddedNov 2, 2026

TDQS

A3.7/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries the full burden and does well: it discloses that data is read from the chain (read-only), that the call is paid, the exact price ($0.01 USDC on Base eip155:8453), and where payment must be placed (params._meta["x402/payment"]). It omits failure behavior — what is returned for an unconfirmed, unknown, or mismatched-recipient hash — which is the main remaining gap.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

One front-loaded sentence covers inputs, outputs and provenance, followed by a compact pricing/payment/endpoint block. Every clause is functional; only the raw HTTP endpoint adds marginal value for an MCP caller.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

There is no output schema, so the description's enumeration of return fields is necessary and present, as is the payment contract required to actually invoke a paid x402 endpoint. Missing are the multi-hash input format and the behavior when a tx is not found or the recipient does not match.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0%, so the description must compensate, and it partly does: 'to' is explained as an optional expected recipient, and 'txs' as Base USDC transfer tx hashes. However, 'txs' is typed as a plain string while the description says 'one or more', leaving the encoding of multiple hashes (comma-separated, JSON array in a string?) ambiguous.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource: verify Base USDC transfer tx hashes, with an optional expected-recipient check. It also enumerates exactly what is returned (status, from/to, amount, block, timestamp, token contract), so the agent knows precisely what it gets. It does not differentiate itself from near-name siblings such as txpreflight__verify or chainread__txpreflight, which keeps it at 4.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is implied rather than stated: the tool is for confirming Base USDC payments against an expected recipient. There is no explicit when-to-use sentence and no direction on when to prefer chainread__payment or txpreflight__verify instead, so the agent must infer the selection rule from the name and scope.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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